Padlocks used with hasps and staples are well known in the art, and are continually being improved. One direction in which such improvements are made is in the use of high security lock cylinders enclosed within the body of the padlock such as are described and shown in U.S. Pat. Nos. 3,499,302 and 3,722,240. Normally such lock cylinders are replaceably fixed in high security padlocks in a manner so that they may be changed in the event that keys become lost or stolen without having to replace the entire padlock.
In replacing lock cylinders in high security padlocks problems arise in connection with securely enclosing the lock cylinder within the padlock body. One method has been to use a separate key for releasing the lock cylinder and another key for opening and closing the padlock. Still other methods have been used wherein the lock cylinder is enclosed by a pin either into the cylinder per se or into a cover plate as for example in U.S. Pat. Nos. 824,593 and 2,047,969. Still another method for securely enclosing the lock cylinder within the padlock body is by use of the shackle providing an interlock with the cover plate as demonstrated in U.S. Pat. Nos. 2,047,969 and 3,710,603. Both of these patents, however, have limitations.
For example, in U.S. Pat. No. 2.047,969 a retaining screw is required which can be tampered with to disable the padlock and in U.S. Pat. No. 3,710,603 the entire shackle becomes free when the padlock is unlocked, giving rise to the padlock per se dropping to the ground and/or the shackle becoming contaminated in normal use of the padlock.